In a few short hours, behind the closed doors of courtroom number one in a nondescript provincial city, China attempted to dispatch its biggest political scandal for two decades.

Thursday's official account of Gu Kailai's trial for the murder of British businessman Neil Heywood raised as many questions as it answered. The number of the room where she is said to have poisoned the Briton was revealed: 1605, at the Lucky Holiday hotel in Chongqing, the southwestern city where Gu's husband Bo Xilai was the powerful party secretary.

But details of Heywood's dealings and economic conflict with Gu remained vague.

And when the black-robed judges return to the Hefei intermediate people's court, at an unspecified date in the near future, they are certain to pronounce Gu and her aide Zhang Xiaojun guilty. The defendants did not contest the allegation of premeditated murder, said Tang Yigan, vice president and spokesman of the court. There was ample evidence that they had "used brutal means" to kill Heywood.

"Gu Kailai is the main culprit and Zhang is the accessory," he said in a statement to reporters.

Yet it went on to note the defence lawyer's claims that the 41-year-old victim, who left a widow and two young children – one, the godchild of his alleged killer – bore "a certain responsibility" for the reason of his murder.

That was presumably a reference to the prosecution claim that Gu thought he posed a threat to her son, Bo Guagua, for reasons not specified.

The case's sensitivity is such that it was not even mentioned in the country's main evening news bulletin. But a short report on the news channel showed Gu, 53, wearing a black suit and white shirt as she arrived in the courtroom.

The former lawyer, who was flanked by two policewomen as she entered, looked considerably heavier than in pictures taken in recent years.

Zhang, her 33-year-old aide, wore a white polo shirt and dark trousers as he walked between two male officers.

Prosecutors alleged that Gu arranged for Zhang to escort Heywood from Beijing to south-western Chongqing on 13 November last year.

She met him in his hotel room, where they drank tea and alcohol together until he was so drunk he vomited and needed water.

She then poured the poison – that she had previously prepared, and that Zhang had carried – into Heywood's mouth.

Gu's lawyer said her ability to control her behaviour was "weaker than normal people's" at the time of the murder, perhaps hinting at mental health issues – though the court noted that she was in good physical condition and emotionally stable during the hearing.

More intriguingly, he said that her "significant contribution" in reporting on other people's crimes should be taken into account. No further details were given.

Whether that was a hint that she might have discussed her husband's affairs – and that he could yet face a criminal trial – is impossible to judge.

"The most important part of the case is still not known – how it relates to Bo Xilai, a Politburo member and rising political star," said Cheng Li, an expert on Chinese elite politics at the Brookings Institution in the US.

Bo was once tipped for possible promotion in the 10-yearly change of leadership approaching this autumn. Now he remains under internal party investigation. Unseen since his ousting in spring, his fate unclear. The challenge for the party is to justify the removal of a popular figure, without discrediting other leaders by association.

"The most important thing [to the party] is making the case that this is truly exceptional. As a murder that's probably true. But the economic issues involved are by no means exceptional; there's widespread corruption," Li said.

Many believe such considerations explain why Gu stood trial solely for murder and why the trial was sited well away from the capital and from Chongqing, where Bo remains popular.

Four police officers from Chongqing were charged last week with covering up Heywood's murder and will stand trial in the same court in Hefei on Friday.

No foreign media were allowed into Gu and Zhang's trial, with officials saying there was no room in the spacious courtroom, although empty seats could be seen in the news footage.

Two British diplomats attended in a consular capacity. Relatives and friends of Heywood and the defendants were present, the statement added.

Dozens of plain clothed officers and scores of uniformed police surrounded the taped-off courthouse throughout the hearing. There were the usual muscular young men with crew cuts and T-shirts. But others, including a woman with a Louis Vuitton handbag and patent leather peep-toe sandals, also wore earpieces as they stood outside the granite-and-glass building in the drenching rain. Two protesters were later dragged away by colleagues at the back of the building.

"The security of the Hefei intermediate court is definitely number one in the world but whether it can ensure just proceedings is another question," lawyer Li Fangping wrote on Sina's Weibo microblog.

Hefei, capital of Anhui province, is known as the home of Lord Bao, an 11th-century official still seen as an icon of justice and righteous officials in China.

But responding to another lawyer's post, the artist and activist Ai Weiwei wrote on Twitter: "The 'justice' of no justice, no fairness, and no openness to the public. It is sad."

Relatives of Gu and Zhang hired lawyers to represent them, only to be told that the defendants had accepted state-appointed lawyers.

Gu thanked the judge, prosecution and defence at the end of proceedings and asked that Zhang receive a lighter sentence than hers, a source who witnessed the trial told the Washington Post.

Possible sentences range from 10 years in prison to the death penalty.

"I committed a crime that brought negative consequences to the party and the country," Gu added, according to the source.

It is unclear whether she extended her concern to the former friend whose violent death, hundreds of miles from his family, had brought her to the courtroom.